Volume 4 Number 2 February 2020 Pages 423–954 Sustainable Energy & Fuels Interdisciplinary research for the development of sustainable energy technologies rsc.li/sustainable-energy ISSN 2398-4902 PAPER Hasan Baig et al. Increasing effi ciency of perovskite solar cells using low concentrating photovoltaic systems Sustainable Energy & Fuels View Article Online PAPER View Journal | View Issue Increasing efficiency of perovskite solar cells using low concentrating photovoltaic systems† Cite this: Sustainable Energy Fuels, 2020, 4,528 Hasan Baig, *a Hiroyuki Kanda,b Abdullah M. Asiri,c Mohammad Khaja Nazeeruddin b and Tapas Mallicka Perovskite solar cell (PSC) technology is the flag bearer for the future of photovoltaics allowing unlimited possibilities for its application. This technology is currently limited by issues related to its scale-up, stability and the composition of the materials used in its preparation. Using small sized solar cells with higher efficiency under solar concentration is gaining traction as a methodology for scaling up this technology and broadening its applications. However, this has only been reported in devices with size <1 mm2 neglecting the series resistance of the device. Here, we report the performance of a 9 mm2 PSC at varying solar concentration levels and correlate it with the series resistance of the solar cell. The n–i–p structured device using a triple cation perovskite absorber with a mesoporous titanium oxide/SnO2 layer as the electron transporting layer and Spiro-OMeTAD as the hole transporting material achieved a peak Creative Commons Attribution 3.0 Unported Licence. efficiency of 21.6% under 1.78 Suns as compared to the 21% obtained under 1 Sun (1000W mÀ2) and AM1.5G. We further boosted the power output up to 15.88 mW under 10.7 Suns compared to the 1.88 mW obtained under 1 Sun; however this results in an actual efficiency drop of the PSC owing to the Received 22nd July 2019 device series resistance. Further, we investigated the impact of the increasing solar cell temperature at Accepted 17th September 2019 higher concentration levels and identified the influence of series resistance on the performance of the DOI: 10.1039/c9se00550a PSC. Our work identifies the potential of concentrating photovoltaics and highlights the challenges and rsc.li/sustainable-energy makes recommendations for future development. This article is licensed under a Introduction limits by using a group of materials stacked together utilising different parts of the solar spectrum and accumulating the Photovoltaic (PV) technology has continued to progress rapidly extracted power.5 Operating solar cells under concentrated ffi 6 Open Access Article. Published on 18 November 2019. Downloaded 10/1/2021 1:44:33 AM. through its growing deployment and the innovation of new sunlight results in an improvement in their e ciency. This is materials. While the global progress of silicon PVs continues to particularly due to the high photon density incident on the solar dominate the industry,1 advanced materials such as perovskite cell which drives larger quasi-Fermi-level splitting in the semi- solar cells (PSCs) are reaching new levels of efficiency making conductor absorber material delivering a higher output voltage them a potential alternative.2 The growth in PSC research is and photovoltaic efficiency of the solar cells.7 8 primarily due to its excellent material properties and ease of By varying the ratio between I and Br in MAPb(IxBr1Àx), the manufacture. The idea of directly printing a high-efficiency PSC bandgap (Eg) of the perovskite material can be tuned from on any given substrate in a variety of shapes and sizes at lower around 1.6 to 2.3 eV and this can be further reduced to 1.2 eV costs opens opportunities for many new PV products and using Sn compositions making them a very good candidate for markets that were previously not possible.3 fabricating multi-junction solar cells.9 The other advantage of The theoretical Shockley–Queisser limit imposed by the these materials is the high absorption coefficient10 and long – material band-gap dictates the electrical efficiency4 of single charge carrier diffusion length.11 13 Whilst higher efficiencies junction solar cells. Multi-junction solar cells overcome these (>21%) for single junction PSCs have been reported, these are predominantly found in smaller sized PSCs (<1 mm2). The use of concentrator photovoltaics (CPVs) with a 0.81 mm2 sized PSC14 aUniversity of Exeter, Environment and Sustainability Institute, University of Exeter, further increased the efficiency levels up to 23.1% opening up Penryn, TR10 9FE, UK. E-mail: [email protected] a new line of research combining PSCs with low concentrating bGroup for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, Ecole´ Polytechnique F´ed´erale de Lausanne, Valais Wallis, photovoltaic (LCPV) technologies. However, the tasks of identi- ff CH-1951 Sion, Switzerland fying the e ectiveness of this methodology and overcoming the cCenter of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz practical challenges remain. In the present study we investigate University, P.O. Box 80203, 21589 Jeddah, Saudi Arabia the performance of a 9 mm2 PSC at low levels of solar concen- † Electronic supplementary information (ESI) available. See DOI: tration and create a new approach that can be realised for 10.1039/c9se00550a 528 | Sustainable Energy Fuels, 2020, 4, 528–537 This journal is © The Royal Society of Chemistry 2020 View Article Online Paper Sustainable Energy & Fuels designing PSCs for LCPV systems. Here, we experimentally eval- quality solar cell with negligible parasitic losses due to series ¼ ¼ N * uate the performance of PSCs both on their own and when and shunt resistances, Rs 0 and Rsh ; Voc is the open coupled with an optical concentrator at different incident illu- circuit voltage (under concentrated light), k is the Boltzmann mination levels and varying solar cell temperatures. The optical constant, and T is the absolute temperature. In an ideal case, concentrator used in this study is a kaleidoscope with a breaking- the short-circuit current is equal to the light-induced current at symmetry top (12 mm  12 mm) and a truncated pyramid load: Isc ¼ IL.  geometry and square exit aperture (3 mm 3 mm). The PSC kT I * – – V * ¼ ln sc used in this study is a triple cation based n i p structured ocðI¼0Þ q I (3) perovskite solar cell.15,16 We observe that the electrical power is O magnied under concentrated sunlight. However, the internal kT À Á V * ¼ ln C þ V series resistance of the solar cell tends to decrease the ll factor ocðI¼0Þ q opt oc (4) substantially. While varying the illumination intensity levels we observe that there exists an optimum solar concentration level for * the solar cell which is a function of its series resistance. There- The Voc as shown in eqn (3) increases logarithmically with fore, it will be possible to design a solar cell for low concentration the increasing photocurrent if the dark current remains levels through the reduction of the series resistance. constant at the cell operating temperature and can be related to the open circuit voltage at standard illumination levels of À 1000 W m 2 and 25 C as per eqn (4). Using the above equa- PSCs under solar concentration tions, the maximum power that can be extracted from the solar Hybrid organic–inorganic lead halide perovskites can combine cell can be expressed as the functions of light absorption, n-type conduction and p-type P* ¼ I *  V *  Max sc oc FF (5) conduction. Fig. 1(a) and (b) describe the absorption of light Creative Commons Attribution 3.0 Unported Licence. leading to the creation of free carriers in a bare PSC and a PSC kT ðCÞ P* ¼ P  C ln Max Max opt (6) with a solar concentrator. Charge separation can then occur q Voc through injection of photo-generated electrons into TiO2 nanoparticles and injection of holes into a hole-transporting material (HTM)17,18 such as Spiro-OMeTAD.19 Concentrated light has a larger number of photons, which accelerates electron Methods generation in the perovskite absorber hence increasing the Perovskite fabrication photo current proportional to the solar concentration (Fig. 1(b)). The fabrication process of a solar cell and the nal architecture This article is licensed under a At a cell voltage of zero, the cell current reaches a maximum are shown in Fig. 2. To prepare the perovskite solar cell, an FTO glass substrate was cleaned by sonication with acetone and limiting value, which is called the short-circuit current (Isc). So, 21 for the short-circuit current of a solar cell under solar concen- ethanol for 15 minute each in order. Then, a blocking titanium tration I* oxide layer (Bl-TiO2) was deposited by spray pyrolysis deposition of Open Access Article. Published on 18 November 2019. Downloaded 10/1/2021 1:44:33 AM. sc a precursor solution (1 mL of titanium diisopropoxide bis(acety- I * ¼ C I sc opt sc (1) lacetonate) (Sigma-Aldrich) in 15 mL of ethanol) and annealed at 450 C as shown in Fig. 2(a).21 To deposit a meso-porous titanium Copt is the optical concentration ratio and eqn (2) explains the lumped equivalent circuit20 model and the application of oxide layer (Mp-TiO2), a dispersed titanium oxide solution (1 g of Kirchoff's rules for this, PST30NRD (Dyesol) in 8 mL of ethanol) was spun on the Bl-TiO2 as shown in Fig. 2(b) and annealed at 500 C(Fig.2(c)). I þ IL V À IRs q ln À þ 1 ¼ ðV À IRsÞ (2) Io IoRsh kT where IL is the current at load, Io is the saturation current, Rs is the series resistance and Rsh is the shunt resistance.